The present invention relates to shielded metal enclosures for electronic components; and specifically to such enclosures for housing an X-ray tube in an imaging system.
An X-ray imaging apparatus includes a vacuum tube with a cathode and anode that emits X-rays upon application of bias voltages to electrodes within the tube. The X-ray tube typically is enclosed in a grounded lead alloy enclosure which act as an X-ray shield. A major problem during the operation of X-ray tubes is high voltage discharge or arcing between the electrodes. The discharges, commonly known as "spits", result from intense electric field gradients caused by contamination or rough edges on the surfaces of the electrodes and occur from time to time during the life of the tube.
The spit discharge excites a resonant cavity tank circuit formed by the X-ray tube and the conductive enclosure, thereby producing a high frequency (3 to 300 megahertz) damped signal. The high frequency signal from a spit discharge is conducted through the case by the electrical conductors that provide power to the tube. Once outside the enclosure, the signal is radiated and conducted throughout the X-ray apparatus and into electronic circuitry in its vicinity. In extreme cases, the electrical signal from the spits causes failure of semiconductor devices in adjacent equipment.